Look up a word with three fingers: the built-in dictionary

An unfamiliar word doesn't have to mean a trip to the browser. macOS has a built-in dictionary, thesaurus, and quick Wikipedia preview, all of which can be summoned right over a word — in any app where you can select text, from PDFs to Mail to Notes.

A typical scenario

A student is reading an academic PDF and runs into an unfamiliar word. The usual route is to open a new browser tab, retype or copy the word, search for it, wait through results full of ads and links — and then come back to the text, often having lost their place.

With the built-in preview, all it takes is hovering the cursor over the word and tapping the trackpad with three fingers. A definition, and possibly a translation, appears right above the text in a small window — the student is reading again within three seconds, with no window switching and no lost focus.

How to do it

1. Hover your cursor over the word whose meaning you want to check — it works in text, mail, a PDF, or a web page.
2. Tap three fingers on the trackpad, or press Ctrl + Cmd + D.
3. A small window pops up with tabs: a dictionary definition, a thesaurus with synonyms, and a Wikipedia preview if it's a proper noun or a known term.
4. Close the window by clicking outside it or pressing Esc — the text underneath stays exactly where it was, no app switching involved.
5. If you have additional language dictionaries installed on your system (Dictionary → Preferences), the preview window switches between them automatically based on the language of the text, or you can pick one manually.
6. The preview also works on a trackpad without a physical click — and in the Dictionary app, you can browse word pronunciations too, if you're curious how a given word is actually said.

The best tools

• The built-in dictionary preview (three-finger tap or Ctrl + Cmd + D) — free, works offline, ideal for a quick meaning check.
• The Dictionary app (Spotlight → "Dictionary") — the same entries in a standalone window, handy for a longer lookup or browsing related terms.
• DeepL or Google Translate — for full sentences and longer passages, where it's not just about one word but understanding the context.
• Dictionary extensions in the browser — for users who mostly read on the web and want the same preview even where the system shortcut doesn't work reliably.

What you get out of it

• Time: no switching to a browser and back — with a text full of unfamiliar words, that adds up to several minutes a week.
• Uninterrupted reading: your attention stays on the text, not broken up by opening new windows and tabs.
• Broader context: besides a definition, you also see synonyms and a short Wikipedia preview, which helps more than a bare definition for technical terms or proper nouns.
• Better comprehension: checking an unfamiliar word quickly, right on the spot, helps a student keep the thread of what they're reading, instead of having to reorient themselves after a browser detour.

Pro tip

It also works on foreign-language words mixed into English text — if you have a bilingual dictionary installed in System Settings, the preview offers a translation right away, so you don't have to switch between a dictionary and a translator app. You can add or remove language dictionaries anytime in System Settings, depending on which languages you work with most.